The Islamic religion was founded by Mohammed in the early 600s. Mohammed's followers believe him to have been the last messenger of God, completing the work of earlier prophets such as Abraham, Moses and Jesus.

Born in the city of Mecca on the Arabian peninsula about 570, Mohammed began in 610 to proselytize for Islam. Islam proclaimed one God and the unity of all people regardless of their tribal affiliation. Opposition in his native Mecca forced Mohammed to remove his base to the city of Medina [then called Yathrib] and even for one period into Abyssinia. As support for Islam flourished, Mohammed assumed secular leadership of Medina.

Finally, after a period of hostility punctuated by warfare, Mohammed in 630 succeeded to the leadership of Mecca as well. Mohammed died two years later in Medina, but the spread of Islam continued unabated, first in the Arab world and then beyond. The emergence of Islam, with its emphasis on the unity of Muslims, dramatically increased the political strength of its followers. The consequences for the Byzantine [Eastern Roman] Empire were immediate, and the implications for Sicily and all of Europe were lasting and profound.